1. Field of the Invention
The present invention relates generally to subsea intervention packages and, more particularly, to a lightweight and compact subsea intervention package.
2. Description of the Background
Often subsea wells do not perform at/to the same levels of performance as platform wells mainly due to the high costs of servicing subsea wells, which may be referred to herein as subsea well interventions. The subsea well Christmas tree, also referred to herein as a production tree, may typically be either a vertical production tree or a horizontal production tree wherein the horizontal subsea production tree may have a larger internal diameter. FIG. 4A, FIG. 4B, FIG. 5A and FIG. 5B show representative examples of vertical and horizontal subsea production or Christmas trees. A subsea intervention package preferably provides a means for connecting the various types of subsea trees to perform workover operations while still maintaining control over the subsea well.
If necessary, a subsea intervention package should provide means to isolate and seal the well in emergency situations, e.g., if a dynamically positioned drilling ship or unanchored semi-submersible platform loses the ability to maintain its position above the subsea well. Emergency disconnect systems should preferably be able to reliably sever any tubing and/or wireline that extends through the Christmas tree and then seal and isolate the well in case it is necessary to disconnect from the well due to an emergency. Prior art systems may be slow to operate to perform these functions and may sometimes allow significant amounts of fluid leakage before isolation is accomplished. It would be more desirable to provide a more effective and environmentally-friendly subsea intervention package.
The maximum internal diameter is a critical dimension for an intervention package because an internal tree plug must normally be retrievable through this dimension. A small increase in the size of the tree plug often results in a significant increase in the size of the intervention package. Horizontal subsea trees tend to have a larger internal diameter tree plug. Crown or tree plugs in horizontal production trees tend to be a maximum of about six and three-quarters inch in diameter and may be considerably less. Due to various construction that may exist around the subsea well it is desirable that the subsea intervention package be compact and not include elements that extend outwardly from the design dimensions of the subsea intervention package. The most commonly utilized subsea intervention package for well completions comprises a high pressure riser system in combination with a subsea drilling BOP and a marine riser for access to the well. This system is very heavy and bulky. A subsea drilling BOP intervention system may weigh in the range of 500,000 to 1,000,000 tons. The system may often require the capabilities of a semi-submersible platform, which may be of the type requiring anchors, to lower and raise the intervention package. Accordingly, the time to move the platform to location and set the anchors is rather long. The bulky system must also be lowered, installed, and then removed. The overall cost of the intervention operation utilizing a subsea drilling BOP intervention system is quite high but the system provides the means for doing any type of desired work.
Other attempts to produce lightweight systems have limitations that make them unsuitable for some types of intervention work.
Consequently, those skilled in the art will appreciate the present invention that addresses the above problems with a lightweight and compact subsea intervention package that can be transported, installed, and then removed from a subsea well more quickly to provide a wide range of operations, and which is operable to cut and seal any working strings therein in a fail-safe mode.